RADIOMETRY
The science of measuring electromagnetic radiation
The practice of Radiometry involves the measurement of electromagnetic radiation in terms of power, or the spatial concentration of radiant power.
Five fundamental types of radiometric measurement may be enumerated, corresponding to five different types of measurement geometry:
| MEASURAND
|
UNITS
| DESCRIPTION
|
| Flux
|
W
| Radiant power (flux) produced by a source
|
| Illuminance
|
W/m2
| Flux incident upon a surface, per unit area
|
| Exitance
|
W/m2
| Flux leaving a surface, per unit area
|
| Intensity
|
W/sr
| Flux leaving a point source, per unit solid angle - measured in steradians (sr)
|
| Luminance
|
W/m2sr
| Flux per unit solid angle leaving an extended source in a given direction, per unit projected area
|
Spectroradiometry involves the analysis of the distribution of these quantities as a function of wavelength, and requires the use of complex multichannel
or scanning instruments. In contrast, Simple Radiometry uses relatively simple, single-channel sensors to measure spectrally-integrated quantities.
Simple radiometry is best suited to the measurement of a source whose radiation is confined to a relatively narrow spectral band.
Such sources include lasers, laser diodes, LEDs, and diode-driven fiber-optic devices.
The forgoing is an overview of key concepts in radiometry, with emphasis on generality and concise description. For a more complete explanation, please consult the UDTi Radiometry Tutorial, and our companion index of resources.
